Devlin's
Angle

September 2006

Statisticians not wanted

On August 16, 2006, the California Supreme Court made it official: in certain legal cases that hinge on statistical calculations, it is not the business of professional statisticians to decide how to evaluate the statistical data and to judge what method is most suited to analyze that data. From now on, in California at least, the courts will decide what statistical analysis is appropriate and what is not.

It gets worse - especially if you are a
professional statistician. By upholding
a ruling by a lower state court, the
California Supreme Court also affirmed
that, in their view, the proper job for
statisticians is simply to plug numbers
into a formula and turn the crank to
produce an answer. Not any formula will
do, mind; if you want your calculation to play a rule in a California legal proceeding, it will have to be the formula chosen by the court. As a professional statistician, you may believe that it is precisely your job to make that call, and that no other profession has the knowledge, expertise, experience, and skill to make such a decision in your stead. But the California Supreme Court says otherwise.
They say the decision is theirs to make.
You don't believe me? Read on.

The issue is one of suspect identification and conviction based on DNA profiling.
Since both the reliability of a "DNA
(profile) match" as a means to identify
a suspect in a criminal investigation
and its efficacy as evidence in court
depend upon the likelihood of two
different individuals sharing the same
profile, use of the technique is crucially dependent on calculation of that likelihood. That's where statistics comes into the picture.

It turns out, however, to be not at
all an obvious matter how to compute
the appropriate statistic - or more
precisely, to decide what exactly
is the appropriate statistic. To
my mind, though not the mind of the
California Supreme Court it appears,
that is where statisticians
should come into the picture.

To take the story any further, I need
to provide a brief summary of the DNA
profiling technique.

DNA profiling

The DNA molecule comprises two long
strands, twisted around each other in
the now familiar double-helix
structure, joined together in a
rope-ladder-fashion by chemical
building blocks called bases. (The
two strands constitute the "ropes" of
the "ladder", the bonds between the
bases its "rungs".) There are four
different bases, adenine (A), thymine
(T), guanine (G), and cytosine (C).
The human genome is made of a sequence
of roughly three billion of these
base-pairs. Proceeding along the
DNA molecule, the sequence of letters
denoting the order of the bases (a
portion might be ... AATGGGCATTTTGAC ...) provides a "readout" of the genetic code of the person (or other living entity). It is this "readout" that provides the basis for DNA profiling.

Using today's techniques, it would be
totally impractical to do a DNA
comparison by determining all three
billion letters. What is done instead
is to examine a very small handful of
sites of variation.

DNA is arranged into large structural
bodies called chromosomes. Humans have
23 pairs of chromosomes which together
make up the human genome. One
chromosome in each pair is inherited
from the mother and the other from the
father. This means that an individual
will have two complete sets of genetic
material. A "gene" is really a location
(locus) on a chromosome. Some genes may
have different versions, which are
referred to as "alleles." A pair of
chromosomes have the same loci all the
way along their length, but may have
different alleles at some of the loci.
Alleles are characterized by their
slightly different base sequences and
are distinguished by their different
phenotypic effects. Some of the genes
studied in forensic DNA tests have as
many as 35 different alleles in the
population.

Most people share very similar gene
sequences, but some regions of DNA
sequence vary from person to person
with high frequency. Comparing
variation in these regions allows
scientists to answer the question of
whether two different DNA samples
come from the same person.

The profiling technique used by the
FBI and other law enforcement
authorities depends on the fact
that the variability is manifested
by differences in the length,
measured by the number of bases or
the number of times a given sequence
repeats, between pre-specified
locations. This procedure yields
two measurements for each sample for
each locus, one for the father's
side and one for the mother's side.
The length of DNA fragments can be
measured precisely. In comparing
two samples at a given locus,
if the pair of measurements from one
sample is the same as the pair of
measurements from the other, the
profiles are said to match at that
locus; otherwise, they are said not
to match at that locus. If the two
profiles match at each of the loci
examined, the profiles are said to
match. If the profiles fail to match
at one or more loci, then the
profiles do not match, and it is
virtually certain that the samples
do not come from the same person.

A match does not mean that the two
samples must absolutely have come from
the same source; all that can be said
is that, so far as the test was able to
determine, the two profiles were
identical, but it is possible for more
than one person to have the same
profile across several loci. At any
given locus, the percentage of
people having DNA fragments of a given
length, in terms of base pairs, is
small but not zero. DNA tests gain
their power from the conjunction of
matches at each of several loci; it
is extremely rare for two samples
taken from unrelated individuals to
show such congruence over many loci.

The FBI's forensic DNA identification
system (called CODIS) examines
thirteen such regions in the genome.
Sequences in these special regions
involve multiple repetitions of short
combinations of letters, such as GATA.
Easily detectable differences
between people lie in the number of
repeats that occur in both copies of
their DNA in these regions. For
example, at one of these regions a
person might have inherited
four repeats (GATAGATAGATAGATA) from
their father and six repeats
(GATAGATAGATAGATAGATAGATA) from
their mother at the same location
in the genome. Another person might
inherit eight repeats
(GATAGATAGATAGATAGATAGATAGATAGATA)
from their father and five repeats
(GATAGATAGATAGATAGATA) from their
mother.

How reliable is DNA profile
matching?

When two randomly chosen DNA samples
match completely in a large number of
regions, such as the 13 used in the
FBI's system, the probability that
they could have come from two
unrelated people is very small.
This fact makes DNA identification
extremely reliable (when performed
correctly). The degree of reliability
is generally measured by using the
product rule of probability theory
to determine the likelihood of
finding a particular profile among
a random selection of the population.

For example, consider a profile
based on just three sites. The
probability that someone would match
a random DNA sample at any one site
is roughly one in ten (1/10). So
the probability that someone would
match a random sample at three
sites would be about one in a
thousand:

1/10 x 1/10 x 1/10 = 1/1,000.

Applying the same probability
calculation to all 13 sites used in
the FBI's CODIS system would mean
that the chances of matching a
given DNA sample at random in the
population are about one in ten
trillion:

(1/10)^13 = 1/10,000,000,000,000.

This figure is known as the random
match probability (RMP). Since it
is computed using the product rule
for multiplying probabilities, it
assumes that the patterns found in
two distinct sites are independent.
Is this assumption justified?
Personally, I find this a particularly
worrying assumption, and it very
definitely is an assumption,
but genetics is not my area of
expertise, and (unlike the
California Supreme Court) I do not
feel comfortable stepping into the
specialties of other professionals.
Overall those specialists seem
reasonably confident in the
independence assumption. In any event,
the courts regularly accept the
independence assumption, and my
present focus lies elsewhere, so
for the purpose of this essay, I'll
simply accept it too.

Using DNA profiling

Here is one way that DNA profiling
is often used in the criminal justice
system. The authorities investigating
a crime obtain evidence that points
to a particular individual as the
criminal, but fails to identify
the suspect with sufficient certainty
to obtain a conviction. If the
suspect's DNA profile is in the
CODIS database, or else a sample is
taken and a profile prepared, it
may be compared with a profile taken
from a sample collected at the
crime scene. If the two profiles
agree on all thirteen loci, then for
all practical - and all legal -
purposes, the suspect is assumed to
have been identified with certainty.
The random match probability (one
in ten trillion) provides an
estimate of the likelihood that
the two profiles came from different
individuals.

Of course, all that a DNA match does
is identify - within a certain degree
of confidence - an individual whose DNA
profile was that same as that of a
sample (or samples) found at the crime
scene. In of itself, it does not imply
that the individual committed the
crime. There could be any number of
ways for a person's DNA to end up at
a crime scene. (If your spouse or
close friend were murdered, very likely
some of your DNA would be found on the
victim's body or clothing. It does
not follow automatically that you are
the killer.) Other evidence is required
to determine guilt of the crime in
question.

As to the degree of confidence that
can be vested in the identification
of an individual by means of a DNA
profile match obtained in the above
manner, the issues to be considered
are:

The likelihood of errors in
collecting (and labeling) the two
samples and determining the
associated DNA profiles

The likelihood that the
profile match is purely coincidental.

A likelihood of one in ten trillion
attached to the second of these two
possibilities (such as is given by
the RMP for a 13-loci match) would
clearly imply that the former
possibility is far more likely,
since hardly any human procedure can
claim a one in ten trillion
fallibility rate. Put differently,
if there is no reason to doubt the
accuracy of the sample collections
procedures and the laboratory
analyses, the DNA profile
identification could surely be
viewed with considerable confidence.

[I have already expressed my doubt
regarding the use of the RMP to
obtain a reliable indicator of
an accidental match, computed as
it is on the basis of our current
scientific understanding of
ggenetics. The RMP calculation
does, after all, require mathematical
independence of the loci - an
extremely demanding condition - in
order to be able to apply the
product rule. I'd feel a lot more
confident if there were some
empirical data to buttress the
accepted assumption.
What empirical data there is seems
if anything to support my doubt. A
recent analysis of the Arizona
convicted offender data base (a
database that uses the 13 CODIS loci)
revealed that among the approximately
65,000 entries listed there were 144
individuals whose DNA profiles match
at 9 loci (including one match between
individuals of different races, one
Caucasion, the other African American),
another few who match at 10 loci, one
pair that match at 11, and one pair
that match at 12. The 11 and 12 loci
matches were siblings, hence not
random. But matches on 9 or 10 loci
among a database as small as 65,000
entries cast considerable doubt in my
mind on figures such as the oft-cited
"one in ten trillion" for a match that
extends to just 3 or 4 additional
loci. But again, this is off my current
target.]

Of course, the a one-in-a-trillion
likelihood figure is massive overkill.
Absent any confounding factors, a
figure of one in a million or one in
ten million (say) would surely be
enough to determine identity with
virtual certainty.

Hence, all of the above cautions
notwithstanding, it seems reasonable
to assume that (blood relatives aside)
a 13-loci match can be taken as
definitive identification - provided
that, and this is absolutely critical
to the calculation and use of the RMP,
the match is arrived at by comparing
a profile from a sample from the
crime scene with a profile taken from
a sample from a suspect who
has already been identified by means
other than his or her DNA profile.
But this is not what happened in
the case that led to the recent
decision by the California Supreme
Court. The case before them involved
a so-called "cold hit identification."

Cold Hit searches

Increasingly, when criminal
investigation authorities find
themselves with crime scene DNA
evidence but no suspects, they resort
to using the DNA profile as a tool
to identify a possible culprit, by
searching DNA profile databases of
previous offenders (such as the
CODIS database) to see if a match can
be found. A "cold hit" identification
is one that results from such a search.
A match obtained in this way would be
a "cold hit" because, prior to
the match, the individual concerned
was not a suspect.

As in the case where DNA profiling is
used to provide identification of an
individual who was already a suspect,
the principal question that has to be
(or at least should be) asked after a
cold hit search has led to a match (a
"hit") is: Does the match indicate
that the profile in the database
belongs to the same person whose
sample formed the basis of the
search, or is the match purely
coincidental? At this point, the
waters rapidly become very murky.

To illustrate the problems inherent
in the Cold Hit procedure, consider
the following analogy. A typical
state lottery will have a probability
of winning a major jackpot around 1 in
35,000,000. To any single individual,
buying a ticket is clearly a waste
of time. Those odds are effectively nil.
But suppose that each week, at least
35,000,000 people actually do buy a
ticket. (This is a realistic example.)
Then every one to three weeks, on
average, someone will win. The news
reporters will go out and interview
that lucky person. What is special
about that person? Absolutely
nothing. The only thing you can say
about that individual is that he or
she is the one who had the winning
numbers. You can make absolutely
no other conclusion. The 1 in
35,000,000 odds tell you nothing
about any other feature of that
person. The fact that there is
a winner reflects the fact that
35,000,000 people bought a ticket
- and nothing else.

Compare this to a reporter who
hears about a person with a
reputation of being unusually
lucky, goes along with them as
they buy their ticket, and sits
alongside them as they watch the
lottery result announced on TV.
Lo and behold, that person wins.
What would you conclude? Most
likely, that there has been a
swindle. With odds of 1 in
35,000,000, it's impossible to
conclude anything else in this
situation.

In the first case, the long odds
tell you nothing about the winning
person, other than that they won.
In the second case, the long odds
tell you a lot.

To my mind, a Cold Hit measured by
RMP is like the first case. All it
tells you is that there is a DNA
profile match. It does not, in of
itself, tell you anything else, and
certainly not that that person is
guilty of the crime.

On the other hand, if an individual
is identified as a crime suspect by
means other than a DNA match, then a
subsequent DNA match is like the
second case. It tells you a lot.
Indeed, assuming the initial
identification had a rational,
relevant basis (like a reputation
for being lucky in the lottery case),
the long RMP odds against a match
could be taken as conclusive. But as
with the lottery example, in order
for the long odds to have (any)
weight, the initial identification
has to be before the DNA comparison
is run (or at least demonstrably
independent thereof). Do the DNA
comparison first, and those impressive
sounding long odds may be totally
meaningless, simply reflecting the
size of the relevant population, just
as in the lottery case.

It has to be admitted that not
everyone agrees with the above
analogy - at least, they do not
agree with the conclusions regarding
the inapplicability of the RMP in
the case of a cold hit match. In
particular, the FBI has argued
repeatedly that the RMP remains
the only statistic that needs
to be presented in court to
provide a metric for the efficacy
of a DNA cold hit match.

Unfortunately, attempts to resolve
the issue by obtaining expert opinion
have so far served only to muddy the
waters still further.

The NRC reports

In 1989, the FBI urged the National
Research Council to carry out a study
of the matter. The NRC formed the
Committee on DNA Technology in
Forensic Science, which issued its
report in 1992. Titled DNA
Technology in Forensic Science,
and published by the National Academy
Press, the report is often referred to
as "NRC I". The committee's main
recommendation regarding the cold hit
process is given on page 124 of the
report:

"The distinction between finding a
match between an evidence sample and
a suspect sample and finding a match
between an evidence sample and one of
many entries in a DNA profile databank
is important. The chance of finding a
match in the second case is
considerably higher. ... The initial
match should be used as probable cause
to obtain a blood sample from the
suspect, but only the statistical
frequency associated with the
additional loci should be presented
at trial (to prevent the selection
bias that is inherent in searching a
databank)."

In part because of the controversy
the NRC I report generated among
scientists regarding the methodology
proposed, and in part because courts
were observed to misinterpret or
misapply some of the statements in
the report, in 1993, Judge William
Sessions, then the Director of the
FBI, asked the NRC to carry out a
follow-up study. A second committee
was assembled, and it issued its
report in 1996. Often referred to
as "NRC II", the second report,
The Evaluation of Forensic DNA
Evidence, was published by the
National Academy Press in 1996.

"Recommendation 5.1. When the
suspect is found by a search of
DNA databases, the random-match
probability should be multiplied
by N, the number of persons in
the database."

The statistic NRC II recommends
using is generally referred to as
the "database match probability",
DMP. This is an unfortunate choice
of name, since the DMP is not a
probability - although in all actual
instances it is a number between 0
and 1, and it does (in my view as
well as that of the NRC II
committee) provide a good
indication of the likelihood of
getting an accidental match when a
cold hit search is carried out.
(The intuition is fairly clear. In
a search for a match in a database
of N entries, there are N chances
of finding such a match.) For a
true probability measure, if
an event has probability 1, then
it is certain to happen. However,
consider a hypothetical case where
a DNA database of 1,000,000
entries is searched for a profile
having a RMP of 1/1,000,000. In
that case, the DMP is

1,000,000 x 1/1,000,000 = 1

However, in this case the
probability that the search will
result in a match is not 1 but
approximately 0.6312.

The committee's explanation for
recommending the use of the DMP to
provide a scientific measure of
the accuracy of a cold hit match
reads as follows:

"A special circumstance arises
when the suspect is identified not
by an eyewitness or by circumstantial
evidence but rather by a search
through a large DNA database. If
the only reason that the person
becomes a suspect is that his DNA
profile turned up in a database,
the calculations must be modified.
There are several approaches, of
which we discuss two. The first,
advocated by the 1992 NRC report,
is to base probability calculations
solely on loci not used in the
search. That is a sound procedure,
but it wastes information, and if
too many loci are used for
iidentification of the suspect,
not enough might be left for an
adequate subsequent analysis. ...
A second procedure is to apply a
simple correction: Multiply the
match probability by the size of
the database searched. This is
the procedure we recommend."
[p.32].

This is essentially the same logic
as I presented for my analogy with
the state lottery.

The controversy

Since two reports by committees
of acknowledged experts in DNA
profiling technology and
statistical analysis, with
each report commissioned by the
FBI, came out strongly against
the admissibility of the RMP, one
might have imagined that would be
the end of the matter, and that
judges in a cold hit trial would
rule in favor of admitting either
the RMP for loci not used in the
initial identification ( la NRC I)
or else ( la NRC II) the DMP but
not the RMP calculated on the full
match.

However, not all statisticians
agreed with the conclusions of the
second NRC committee. Most notably,
Dr. Peter Donnelly, Professor
of Statistical Science at the
University of Oxford, took a
view diametrically opposed to that
of NRC II. In an affidavit to the
Court of the District of Columbia,
in connection with a cold hit case
(the Jenkins case), titled "DNA
Evidence after a database hit" and
dated October 3, 2004, Donnelly
observed that during the preparation
of the NRC II report, he had
substantive discussions about the
issues with four members of the
committee whom he knew
professionally, and went on to say:

"I had argued, and have
subsequently argued, that after a
database search, the DNA evidence ...
is somewhat stronger than in the
setting in which the suspect is
identified by non-DNA evidence
and subsequently found to match
the profile of the crime sample. ...
I disagree fundamentally with the
position of NRC II. Where they
argue that the DNA evidence
becomes less incriminating as the
size of the database increases, I
(and others) have argued that in
fact the DNA evidence becomes
stronger. ... The effect of the
DNA evidence after a database
search is two-fold: (i) the
individual on trial has a profile
which matches that of the crime
sample, and (ii) every other
person in the database has been
eliminated as a possible
perpetrator because their DNA
profile differs from that of the
crime sample. It is the second
effect, of ruling out others,
which makes the DNA evidence
stronger after a database
search..."

Donnelly advocated using a Bayesian
analysis to determine the
probability of a random match,
which method he outlined in
a paper co-written with David
Balding in 1996, titled "Evaluating
DNA Profile Evidence When the
Suspect is Identified Through a
Database Search" (J. Forensic
Science 603) and again in a
subsequent article co-written
with Richard Friedman: "DNA
Database Searches And The Legal
Consumption Of Scientific Evidence",
Michigan Law Review, 00262234, Feb99,
Vol. 97, Issue 4.

The statistic generated by the
Donnelly/Balding method is
generally close to the RMP,
although it results from a very
different calculation.

The Donnelly/Balding method was
considered by NRC II and expressly
rejected. (Readers knowledgable in
probability theory will recognize
at once that this is yet another
manifestation of the ongoing
debate between frequentist and
Bayesian approaches to probability
calculations.)

We thus have a fascinating situation:
two groups of highly qualified experts
in statistical reasoning, each
proposing a different way to
calculate the likelihood that
a cold hit search will identify
an innocent person, and each
claiming that its method
is correct and the other is dead
wrong.

Scarcely any wonder then that the
courts have become confused as to
what number or numbers should be
presented in court as evidence.

Personally, I (together with the
collective opinion of the NRC II
committee) find it hard to accept
Donnelly's argument, but his view
does seem to establish quite
clearly that the relevant scientific
community (in this case statisticians)
have not yet reached consensus on
how best to compute the reliability
metric for a cold hit.

As I understand it (as a non-lawyer),
the accepted procedure for the courts
to follow when there is no consensus
regarding a scientific procedure is to
rule inadmissible the introduction as
evidence of results obtained by the
disputed procedure. In this case, that
would, I believe, make it very difficult to provide the RMP as the sole numerical indicator of the reliability of a DNA profile match obtained from a cold hit search, a state of affairs that the FBI, for one, appears to wish not to happen.

The question then is, what should the
courts do? My personal view, as a
mathematician, is that they should
adopt one of the approaches recommended
by the NRC, preferably NRC I (which is
free of controversy), taking advantage
of much improved DNA testing technology
to extend the match process to more than
13 loci, a move that would more than
compensate for the increase in the
accidental match probability,
however it is calculated, that
results from a cold hit search.

What the courts should definitely not
do, in my opinion (and let me stress
that what you are reading is, as always
in "Devlin's Angle", an opinion), is
simply take it upon itself to decide,
as a matter of law rather than
scientific accuracy, which calculation
should be used. That is not how the
courts normally act in matters of
scientific evidence, and in my view
it is not how they should act here.

Yet this is exactly what the California
Supreme Court has just done with its
recent ruling. (The decision went 4 to
2 with one justice recusing himself.
The court did not give the reasoning
behind their decision.)

Two test cases

There are, to my knowledge, two cases
currently before the California courts
where there is dispute as to the
admissibility of cold hit calculations,
one of which led directly to the
recent decision.

In one, People of the State of California versus Christopher Goree, the Los Angeles District Attorney, in his submission to the Los Angeles Superior Court dated 5/19/06, opposed the defendant's motion to exclude DNA cold hit statistics resulting from a method currently in dispute, stating ". . .any argument regarding the relevance in a 'cold hit case' of a rarity/random match probability statistics is a legal argument, not a [. . .] scientific argument."

Statisticians reading this may be
shocked, but the DA meant what he said.
Later in his motion, he argues:
"Whether evidence has less probative
value or more probative value is a legal evaluation, not a scientific one. Nothing prevents scientists from debating the issue, but its evaluation and resolution is reserved for the judiciary alone."

While the first sentence in the above
claim may well be correct from a legal
standpoint, think very carefully about
what is implied by the second sentence.
We are, after all, talking here not
about opinions, but what number, as
a matter of actual fact, most accurately measures the mathematical likelihood of a false conviction. The fact that at present different groups of statisticians do not agree on the answer does not make this any less a matter of actual fact. It just means that the relevant professional community have not yet reached consensus on what that actual fact is.

This kind of thing is hardly unknown
in science. Physicists are currently in
disagreement as to whether string theory correctly describes the universe we live in.
But should that too be a matter for the
courts to resolve?

Yes, of course the courts are where
decisions must be made as to what
evidence may or may not be admitted.
But when that evidence is a result of
the application of science, they should
do so in an informed way, upon the
advice of the appropriate scientists.
In that case of cold hit DNA cases, that means professional statisticians.
If the statisticians agree on a number
or numbers that describe a certain
situation, the court must, if it decides such numbers are relevant, use that number or numbers - and definitely no others. If the statisticians express disagreement, the court would be wise to act on the assumption that either view may be correct. (Correct here does not mean which calculation is correct as a calculation. In the present cold hit controversy, no one argues that any particular calculation is incorrect.
Rather, the "correctness" in dispute
is which calculation (and hence the
result of that calculation) best
describes the actual situation before
the court.)

The LA District Attorney goes on to say:
"Defendant then postulates that when a
single suspect is identified in a DNA
database search, the significance of a
subsequent one-to-one DNA profile
comparison between the suspect and the
perpetrator should not be described
using the rarity/ransom match probability in the general population. He is wrong, however. [ . . . ] The exact means by which the suspect was initially identified are irrelevant."

I know of no statistician, be he or
she frequentist or Bayesian, who would
agree to that last claim. Still, the DA
is trying to secure a conviction. It
is not his job to be faithful to
science, rather to make the best case
he can. What I find far more worrying
are the decisions being made by the
courts. For their job, after all, is
to get at the truth.

In the second case I shall discuss, The
People versus Michael Johnson, the Court of Appeal of the State of California Fifth Appellate District issued an opinion on May 25 of this year, in which they
state: "In our view, the means by which
a particular person comes to be suspected of a crime - the reason law enforcement's investigation focuses on him - is irrelevant to the issue to be decided at trial, i.e., that person's guilt or innocence."

The court continues a short while later:
" . . . the fact that here, the genetic
profile from the evidence sample (the
perpetrator's profile) matched the profile of someone in a database of criminal offenders, does not affect the strength of the evidence against appellant.
[ . . . ] The fact appellant was first
identified as a possible suspect based on a database search simply does not matter."

Oh dear, oh dear, oh dear.

Again, I urge you to play out the above
line of reasoning with my lottery example.
Every week, millions and millions of
lottery entrants are reminded of the huge difference between "the probability that someone will win" and "the probability that YOU will win."

Subsequent to the court's opinion on
the Johnson case, I was one or several
scientists who wrote an Amicus Brief to
the California Supreme Court requesting
that in cold hit cases as in other cases involving scientific issues, the courts should seek expert opinion from, in this case, statisticians.

[Incidentally, my only involvement in
the general issue of probability
calculations in DNA cold hit cases
is that of a citizen concerned that
justice be properly done, and a
mathematician who believes I have
a duty to ensure that the professional
opinion of mathematicians should be
taken into account when it is relevant.
I have no connection with any case
currently before the courts, and know
nothing about any of them other than
is available in public documents. I have no personal interested vested in whether the court accepts or denies a brief to which I am a cosignator.]

In our brief, we state:

By way of background, we make clear
that we are scholars and scientists,
not attorneys. Our professional
interest is in the proper
understanding of the role that
science in general, and statistics
in particular, can and should play
in legal cases involving forensic
DNA evidence. Assuming that
criminal trials are a search for
the truth, evidence presented
before juries should be accurate.
Forensic DNA evidence is grounded
in statistical expressions that
measure the likelihood of
coincidence. Statisticians and
other professional scientists with
an interest in, and knowledge
about, statistics and genetics
are uniquely empowered to advise
how to derive those statistical
expressions. Science matters,
and court decisions that treat
statistical questions such as how
to express match evidence in DNA
database match cases as purely
legal ones are, respectfully,
irresponsible."

By denying the petition for review
in the Johnson case of which our
brief was part, the California
Supreme Court has ruled that, for
now at least, it is for the courts
to decide which statistical
calculations to accept and which to
keep out in cold hit cases. That
strikes me as a scandalous afront
to all professional statisticians,
both those who regularly testify
for the prosecutions and those who
testify for the defendants in DNA
profile cases.

Given the system of checks and balances
in our legal system, I am hopeful that
in due course the matter will be resolved correctly. In the meantime, I fear that the very DNA profiling procedure that has been used so successfully to overturn many previous false convictions (as well as put behind bars individuals I for one am glad are no longer roaming the streets), will, in the case of cold hit cases as currently being adjudicated, lead to another collection of wrongful convictions that later courts will have to undo.